Since a photographic process using silver halide is excellent in photographic characteristics such as sensitivity, gradation control, etc., as compared to other photographic processes such as electrophotographic process and diazo photographic process, the silver halide photographic process has hitherto been most widely used. Recently, a technique capable of more easily and rapidly obtaining images has been developed by changing an image-forming process by a light-sensitive material using silver halide from a conventional wet process such as a process by a liquid developer to a dry process such as a developing process by heating
Heat developable light-sensitive materials are known in the field of the art and the heat developable light-sensitive materials and image-forming processes using these light-sensitive materials are described in, for example, U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, 3,457,075, British Patents 1,131,108, 1,167,777, and Research Disclosure, (RD-17029), June 1978, pages 9-15.
Also, for obtaining color images, various processes are proposed as illustrated below.
For example, dyes and bleaching processes useful for a process of forming positive color images by a silver dye bleaching process utilizing heat is described in, for example, Research Disclosure (RD-14433), April 1976, pages 30-32, ibid., (RD-15227), December 1976, pages 14-15, U.S. Pat. No. 4,235,957, etc. However, the foregoing process has the faults that an additional step of superposing an activating agent-containing sheet for accelerating a bleach of dye onto the heat developing light-sensitive material followed by heating is required and also the color images obtained are gradually bleached due to the reduction function of free silver existing together with the color images during the preservation of the light-sensitive material for a long period of time.
Also, a process of forming color images utilizing leuco dyes is described in, for example, U.S. Pat. Nos. 3,985,565 and 4,022,517. However, this process has such faults that the stable incorporation of leuco dyes in a photographic material is difficult and also the photographic material is gradually colored during the preservation thereof.
Furthermore, a process of introducing a nitrogen-containing heterocyclic ring to a dye, forming a silver salt, and liberating the dye by heat development is described in Research Disclosure (RD-16966), May 1978, pages 54-58. However, in the process it is difficult to control the liberation of the dye at unexposure areas and hence the process is unsuitable for a general process.
Moreover, for a process of forming color images by a combination of the oxidation product of a developing agent and couplers, a combination of a p-phenylenediamine series reducing agent and a phenolic or active methylene coupler is described in U.S. Pat. No. 3,531,286; p-aminophenol series reducing agents are described in U.S. Pat. No. 3,761,270; sulfonamidophenol series reducing agents are described in Belgian Patent 802,519 and Research Disclosure (RD-13742), September 1975, pages 31 and 32, and a combination of a sulfonamidophenol series reducing agent and a 4-equivalent coupler is described in U.S. Pat. No. 4,021,240. However, these processes have such a fault that color images formed become turbid since the images of reduced silver and color images are simultaneously formed at the exposure areas after heat development.
Furthermore, in these conventional processes there is a fault that the reducing agent is oxidized by the unreacted silver halide at unexposure areas and the oxidation product is reacted with couplers to increase fogs.
The inventors previously proposed a novel light-sensitive material which can overcome the difficulties in these conventional processes (see, Japanese Patent Application (OPI) No. 149046/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")). The light-sensitive material is a diffusion transfer type heat developable light-sensitive material comprising a support having thereon at least a light-sensitive silver halide, a hydrophilic binder, a reducing agent to the silver halide, and a non-diffusible 2-equivalent coupler and color images having high quality can be obtained by heating the light-sensitive material after imagewise exposure or simultaneously with imagewise exposure, and transferring the mobile dye thus formed imagewise into a dye fixing layer with supplying a solvent mainly from outside.